As president, he sought to modernize the American economy and promoted education. Adams enacted a part of his agenda and paid off much of the national debt. He was stymied by a Congress controlled by his enemies, and his lack of patronage networks helped politicians eager to undercut him. He lost his 1828 bid for re-election to Andrew Jackson. In doing so, he became the first president since his father to serve a single term.

Adams is best known as a diplomat who shaped America's foreign policy in line with his ardently nationalist commitment to America's republican values. More recently Howe (2007) portrayed Adams as the exemplar and moral leader in an era of modernization. During Adams' lifetime, technological innovations and new means of communication spread messages of religious revival, social reform, and party politics. Goods, money, and people traveled more rapidly and efficiently than ever before.

Adams was elected a U.S. Representative from Massachusetts after leaving office, serving for the last 17 years of his life with far greater acclamation than he had achieved as president. He is, so far, the only president later elected to the United States House of Representatives. Animated by his growing revulsion against slavery, Adams became a leading opponent of the Slave Power. He predicted that if a civil war were to break out, the president could abolish slavery by using his war powers. Adams also predicted the Union's dissolution over the slavery issue, but said that if the South became independent there would be a series of bloody slave revolts.